Yes, I went with the flow and upgraded all my systems to Windows 10. In the beginning it felt good, but as time has passed, I have come to realize that some of the work related software does not work well in Windows 10 as much as it used to work in Windows 7. The same is true for hardware that I had bought a couple of years ago. For example, my good old Canon printer that has been working without any problems in Windows 7 shows some glitches in Windows 10 even after using the driver software meant for Windows 10. So I decided to make one of my computer a dual-boot computer that can boot both into Windows 10 and Windows 7. It turned out that nothing can be easier than installing Windows 7 in dual boot configuration after installing Windows 10.
First of all, you have to create a partition to be used for installing Windows 7. You can use MiniTool Partition Wizard free edition to use some space from existing partitions and create a new partition for Windows 7. This can be done using the partition-split function in Partition Wizard. You have to create an extended/logical partition having at least 30 GB space for optimal performance.
If you are installing 32-bit Windows 7 after installing 64-bit or 32-bit Windows 10 (OR if you are installing 64-bit Windows after installing 64-bit Windows 10), then all you have to do is insert the Windows 7 installation DVD/USB disk and launch the setup right from inside Windows 10. Follow the on-screen instructions, choose the newly created partition for installing Windows 7 and it will install Windows 7 in dual boot configuration automatically. Your PC will reboot multiple times during the installation and Windows 7 will be set as your default boot OS.
If you are installing 64-bit Windows 7 after installing 32-bit Windows 10, then you cannot run the setup from within Windows 10. You will have to boot from the Windows 7 installation media and follow the installation instructions from there. Be careful during the installation and choose the newly created partition for installing Windows 7. In the end, you would have dual boot Windows PC with choice of booting into Windows 7 or Windows 10.
You can configure the dual boot menu that is displayed at the boot later from within Windows 7 or Windows 10. For this you have to open the system properties (Win+Pause), click on Advanced System Settings and then click on the Settings button for Startup and Recovery. From the window that opens up, you can choose the default OS (Windows 7 or Windows 10) and the time to display the boot menu (by default it is 30 seconds).
Conclusion: Installing Windows 7 after installing Windows 10 in the dual boot configuration is as easy as attaching the Windows 7 install media into your PC. In less than 30 minutes, you will have Windows 10 and Windows 7 both available at the boot menu in your PC.